.back-to-top-btn {
  position: fixed;
  bottom: 30px;
  left: 50%;
  transform: translateX(-50%);
  width: 50px;
  height: 50px;
  border-radius: 50%;
  background: linear-gradient(135deg, #667eea 0, #764ba2 100%);
  border: none;
  color: #fff;
  cursor: pointer;
  display: none;
  align-items: center;
  justify-content: center;
  box-shadow: 0 4px 15px rgba(102, 126, 234, 0.4);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  z-index: 999;
  padding: 0;
  font-size: 0;
}
.back-to-top-btn:hover {
  background: linear-gradient(135deg, #764ba2 0, #667eea 100%);
  box-shadow: 0 6px 20px rgba(102, 126, 234, 0.6);
  transform: translateX(-50%) translateY(-3px);
}
.back-to-top-btn:active {
  transform: translateX(-50%) translateY(-1px);
  box-shadow: 0 3px 10px rgba(102, 126, 234, 0.4);
}
.back-to-top-btn.show {
  display: flex;
  animation: slideUp 0.3s ease-out;
}
.back-to-top-btn.hide {
  animation: slideDown 0.3s ease-out forwards;
}
.back-to-top-icon {
  width: 24px;
  height: 24px;
  stroke-width: 2.5;
}
@keyframes slideUp {
  from {
    opacity: 0;
    transform: translateX(-50%) translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateX(-50%) translateY(0);
  }
}
@keyframes slideDown {
  from {
    opacity: 1;
    transform: translateX(-50%) translateY(0);
  }
  to {
    opacity: 0;
    transform: translateX(-50%) translateY(20px);
  }
}
html {
  scroll-behavior: smooth;
}
@media (max-width: 768px) {
  .back-to-top-btn {
    width: 45px;
    height: 45px;
    bottom: 20px;
  }
  .back-to-top-icon {
    width: 20px;
    height: 20px;
  }
}
@media (max-width: 480px) {
  .back-to-top-btn {
    width: 40px;
    height: 40px;
    bottom: 15px;
  }
  .back-to-top-icon {
    width: 18px;
    height: 18px;
  }
}